1. Field of the Invention
This invention relates to an optical information processing apparatus for performing recordation and reproduction of information on an optical recording medium, and more particularly to an optical pickup using an optical waveguide, and an optical information processing apparatus using the optical pickup.
Here in this specification, "processing information" means reproducing and/or recording information on an optical recording medium.
2. Description of the Related Art
Heretofore, in an effort to minimize access time of an optical information recording apparatus, an optical pickup was proposed by Japanese Patent Laid-Open Publication No. 129938/1985, in which an SAW (Surface Acoustic Wave) light deflector is located on an optical waveguide and tracking is performed with no mechanical movable part, thus reducing a micro seek time sharply. This system has a structure such as shown in FIGS. 12A and 12B. In the optical pickup of FIGS. 12A and 12B, light emitted from a semiconductor laser 1 is introduced into an optical waveguide layer 3, which is formed on a substrate 2, according to an end-surface connecting method. The light beams that have been made parallel according to a geodesic or mode-index type coupling lens 7 are diffracted due to a SAW (Surface Acoustic Wave) generated when a high-frequency a.c. voltage is applied to an SAW electrode 5, and are focused on an optical disk substrate 4 by a diffraction grating objective lens 8, thus forming a light spot 11. Return light beams run through the objective lens 8, the SAW 6 and the coupling lens 7 and are then bent by a bend diffraction grating 9 to reach a quartered optical sensor 10.
Focusing is provided as follows by Foucault's method: EQU S.sub.focusing =(D.sub.a +D.sub.d)-(D.sub.b +D.sub.c)=0.
Tracking is also provided as follows by the push-pull method: EQU S.sub.tracking =(D.sub.a +D.sub.b)-(D.sub.c +D.sub.d)=0.
Further, a detection signal is obtained as follows: EQU S.sub.signal =D.sub.a +D.sub.b +D.sub.c +D.sub.d =0.
By varying the frequency of a.c. voltage to be applied to the SAW electrode 5, the light spot 11 is moved in the direction of x, namely, radially of the optical disk substrate 4 to perform micro seek and tracking control.
In this prior art, because of the structure of the SAW light deflector, the number of the light spots focused and formed on the optical recording medium would be one. As advances have recently been made on performance of optical information recording apparatuses, the need to form plural light spots on the optical recording medium such as by adapting the tracking error detecting method, which is a three spot method resistant to surface vibration of a disk, by the multiple beam method, which enables to check erasing, recording and reproducing immediately after recording, or by the multiple channel method to improve the transfer rate of data.
However, since the SAW light deflector of the prior art can be dealt with only a single light spot, it would necessarily require as many SAW light deflectors as the number of light spots. Because the size of the individual SAW light deflector must be restricted, it is difficult to produce plural light spots close to one another. Therefore, for plural light spots, this kind of SAW light deflector cannot be used, and mechanical deflectors such as rotary mirrors must necessarily be used.
Consequently, with the prior art, it was difficult to reduce a micro seek time when forming plural light spots on the optical recording medium. This will be discussed more in connection with FIG. 4.
In FIG. 4, reference numeral 2 designates a substrate; 3, an optical waveguide layer; 5, an SAW electrode; 5a, an exciter circuit; and 6, an SAW. For introducing plural light beams into the optical waveguide layer 3, it is necessary to use collimated light beams 13a, 13b, 13c, whose angles are slightly different from one another, in view of the characteristic of the optical waveguide. The light beams emitted from the optical waveguide layer 3 by a linear grating coupler 14 run through a diffraction grating 15 for correcting fluctuations of wavelength, a prism 16 and an objective lens 8 to form light spots 11a, 11b, 11c on a single row. At that time, deflection of light beams by the SAW 6 occur within the plane of the optical waveguide layer and, as a result, the direction of scanning the light spots 11a, 11b, 11c is aligned with the direction y of arrangement of the light spots.
Therefore, with the prior art, it was impossible to detect a tracking error of the three-spot method requiring plural light spots, to form plural light spots on one and the same track such as by the multi-beam method, and to scan the plural light spots perpendicularly to the row of the light spots.
Further, in the multi-channel method, as shown in FIG. 11, since the light spots 11a, 11b, 11c are spaced from one another by more than the intertrack distance, they would be formed on the tracks 12a, 12b, 12c spaced from one another by several to tens tracks. Therefore, in the prior art, it was not impossible to arrange plural light spots on adjacent tracks.